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Ara Nazarian

Publications and source records attributed to Ara Nazarian.

10 recordsLinked to original sources
PubMed2026

In Vivo Base Editing Partially Rescues Bone Dysplasia in a Mouse Model of Hutchinson-Gilford Progeria Syndrome.

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder affecting tissues of mesenchymal origin. Most patients harbor a c.1824C>T/p.G608= variant, commonly described as G608G, in exon 11 of LMNA that leads to aberrant splicing and production of the toxic progerin protein. In addition to cardiovascular, dermal, and adipose tissue deterioration, HGPS mouse models also develop progressive bone dysplasia that occurs in patients. Here we characterize the efficacy of in&#xa0;vivo mutation correction with an adenine base editor (ABE) to rescue structural and functional defects in HGPS transgenic murine bone tissue. Treatment of double-copy transgenic osteoblast cultures with a lentiviral-delivered CRISPR-Cas9 ABE achieved nearly 40% gene correction in&#xa0;vitro, resulting in significant reduction of progerin transcripts and protein, in the absence of selective agents. Furthermore, gene correction improved progeroid osteoblasts' capacity to deposit and mineralize extracellular matrix compared to untreated cultures. In&#xa0;vivo, a single intravenous dose of AAV9-delivered ABE corrected the mutation, achieving ~14%, ~22%, ~10% and <&#x2009;1% correction in bone by six months of age when administered at P3, P14, 1 and 4&#x2009;months of age, respectively. Partially rescued bone structural and physical parameters were observed in P14-treated mice with concomitant normalization of gene transcriptional programs and intracellular signaling pathways involved in bone remodeling. This work demonstrates in&#xa0;vivo delivery of a locus-specific DNA base editor to bone tissue, delineates the timing of treatment required for maximum efficacy, and suggests that this system might be tailored for application to other monogenic bone disorders.

Animals↗
PubMed2006

The interaction of microstructure and volume fraction in predicting failure in cancellous bone.

Inroads have been made in the diagnosis and treatment of osteoporosis, yet dual-energy X-ray absorptiometry is still the primary diagnostic modality. This method provides 2D projections of an irregular 3D construct. However, human cancellous bone is highly heterogeneous with varying material properties. Therefore, to properly assess fracture risk, it is imperative to take into consideration microstructural indices besides subregional bone volume fraction (BV/TV). A power law model with average BV/TV as the independent variable describes 38% of the variation in yield strength; however, this predictive power is increased to 56% when BV/TV of the weakest subregion is considered. Of twenty-five specimens studied, 76% had minimum BV/TV, maximum principal Eigen value of the fabric tensor (H1) and minimum connectivity density (Conn.D) values within the visually determined failure regions. These three independent morphometric indices yielded significant differences between the failure and non-failure regions of each specimen. From the results, we conclude that subregions with minimal BV/TV values are better predictors of mechanical failure in cancellous bone than average specimen BV/TV. Addition of microstructural indices augments this predictive power to generate a trabecular failure prediction model based on volume fraction and cancellous bone microstructure specifically in areas where trabecular failure is most likely to occur.

Aged↗
PubMed2006

Direct percutaneous gene delivery to enhance healing of segmental bone defects.

BACKGROUND: Healing of segmental bone defects can be induced experimentally with genetically modified osteoprogenitor cells, an ex vivo strategy that requires two operative interventions and substantial cost. Direct transfer of osteogenic genes offers an alternative, clinically expeditious, cost-effective approach. We evaluated its potential in a well-established, critical-size, rat femoral defect model. METHODS: A critical-size defect was created in the right femur of forty-eight skeletally mature Sprague-Dawley rats. After twenty-four hours, each defect received a single, intralesional, percutaneous injection of adenovirus carrying bone morphogenetic protein-2 (Ad.BMP-2) or luciferase cDNA (Ad.luc) or it remained untreated. Healing was monitored with weekly radiographs. At eight weeks, the rats were killed and the femora were evaluated with dual-energy x-ray absorptiometry, micro-computed tomography, histological analysis, histomorphometry, and torsional mechanical testing. RESULTS: Radiographically, 75% of the Ad.BMP-2-treated femora showed osseous union. Bone mineral content was similar between the Ad.BMP-2-treated femora (0.045 +/- 0.020 g) and the contralateral, intact femora (0.047 +/- 0.003 g). Histologically, 50% of the Ad.BMP-2-treated defects were bridged by lamellar, trabecular bone; the other 50% contained islands of cartilage. The control (Ad.luc-treated) defects were filled with fibrous tissue. Histomorphometry demonstrated a large difference in osteogenesis between the Ad.BMP-2 group (mean bone area, 3.25 +/- 0.67 mm(2)) and the controls (mean bone area, 0.65 +/- 0.67 mm(2)). By eight weeks, the Ad.BMP-2-treated femora had approximately one-fourth of the strength (mean, 0.07 +/- 0.04 Nm) and stiffness (mean, 0.5 +/- 0.4 Nm/rad) of the contralateral femora (0.3 +/- 0.08 Nm and 2.0 +/- 0.5 Nm/rad, respectively). CONCLUSIONS: A single, percutaneous, intralesional injection of Ad.BMP-2 induces healing of critical-size femoral bone defects in rats within eight weeks. At this time, the repair tissue is predominantly trabecular bone, has normal bone mineral content, and has gained mechanical strength.

Animals↗
PubMed2005

Design and implementation of a novel mechanical testing system for cellular solids.

Cellular solids constitute an important class of engineering materials encompassing both man-made and natural constructs. Materials such as wood, cork, coral, and cancellous bone are examples of cellular solids. The structural analysis of cellular solid failure has been limited to 2D sections to illustrate global fracture patterns. Due to the inherent destructiveness of 2D methods, dynamic assessment of fracture progression has not been possible. Image-guided failure assessment (IGFA), a noninvasive technique to analyze 3D progressive bone failure, has been developed utilizing stepwise microcompression in combination with time-lapsed microcomputed tomographic imaging (microCT). This method allows for the assessment of fracture progression in the plastic region, where much of the structural deformation/energy absorption is encountered in a cellular solid. Therefore, the goal of this project was to design and fabricate a novel micromechanical testing system to validate the effectiveness of the stepwise IGFA technique compared to classical continuous mechanical testing, using a variety of engineered and natural cellular solids. In our analysis, we found stepwise compression to be a valid approach for IGFA with high precision and accuracy comparable to classical continuous testing. Therefore, this approach complements the conventional mechanical testing methods by providing visual insight into the failure propagation mechanisms of cellular solids.

Aluminum↗
PubMed2004

Time-lapsed microstructural imaging of bone failure behavior.

Many bones within the axial and appendicular skeleton are subjected to repetitive loading during the course of ordinary daily activities. If this loading is of sufficient magnitude or duration, failure of the bone tissue may result. Until recently the structural analysis of these fractures has been limited to two-dimensional sections. Due to the inherent destructiveness of this method, dynamic assessment of fracture progression has not been possible. An image-guided technique to analyze structural failure has been developed utilizing step-wise micro-compression in combination with time-lapsed micro-computed tomographic imaging. This technique allows, for the first time, direct three-dimensional visualization and quantification of fracture initiation and progression on the microscopic level and relates the global failure properties of trabecular bone to those of the individual trabeculae. The goals of this project were first to design and fabricate a novel micro-mechanical testing system, composed of a micro-compression device and a material testing and data acquisition system; and second, to validate the testing system to perform step-wise testing of trabecular bone specimens based on image-guided failure analysis. Due to the rate dependant properties of bone, stress relaxation was a concerning factor with respect to the step-wise testing method. In order to address these concerns, the results of the step-wise testing method were compared to those obtained from a conventional continuous test (considered to be the gold standard for the step-wise compressive mechanical testing) over the same total strain range and testing conditions. This was performed using porous aluminum alloy samples with highly reproducible and homogenous structural properties as well as trabecular bone samples from a single whale vertebra. Five cylinders from aluminum foam and trabecular whale bone each were compressed and imaged in a step-wise fashion from 0% to 20% strain at intervals of 2%, 4%, 8%, 12%, 16% and 20%. Mechanical properties obtained from the continuous and step-wise methods were not significantly different for both aluminum foam and whale bone specimens (p>0.05). Both testing methods yielded very similar stress-strain graphs with almost identical elastic and plastic regions with overlaying standard error bars for both whale bone and aluminum foam specimens. This was further concurred by performing regression analyses between the stress data from both testing methods (r(2)=0.98 for whale bone and aluminum foam specimens). Animations of fracture initiation and progression revealed that failure always occurred in local bands with the remaining regions of the structure largely unaffected independent of structure type. In conclusion, we found step-wise micro-compression to be a valid approach for image-guided failure assessment (IGFA) with high precision and accuracy as compared to classical continuous testing. We expect findings from upcoming studies of IGFA of human vertebral bone to improve our understanding of the relative importance of densitometric, morphological, and loading factors in the etiology of spontaneous fractures of the spine. Eventually, this improved understanding may lead to more successful approaches to the prevention of age-related fatigue fractures.

Animals↗
PubMed2003

Megakaryocyte-osteoblast interaction revealed in mice deficient in transcription factors GATA-1 and NF-E2.

UNLABELLED: Mice deficient in GATA-1 or NF-E2 have a 200-300% increase in bone volume and formation parameters. Osteoblasts and osteoclasts generated in vitro from mutant and control animals were similar in number and function. Osteoblast proliferation increased up to 6-fold when cultured with megakaryocytes. A megakaryocyte-osteoblast interaction plays a role in the increased bone formation in these mice. INTRODUCTION: GATA-1 and NF-E2 are transcription factors required for the differentiation of megakaryocytes. Mice deficient in these factors have phenotypes characterized by markedly increased numbers of immature megakaryocytes, a concomitant drastic reduction of platelets, and a striking increased bone mass. The similar bone phenotype in both animal models led us to explore the interaction between osteoblasts and megakaryocytes. MATERIALS AND METHODS: Histomorphometry, microCT, and serum and urine biochemistries were used to assess the bone phenotype in these mice. Wildtype and mutant osteoblasts were examined for differences in proliferation, alkaline phosphatase activity, and osteocalcin secretion. In vitro osteoclast numbers and resorption were measured. Because mutant osteoblasts and osteoclasts were similar to control cells, and because of the similar bone phenotype, we explored the interaction between cells of the osteoblast lineage and megakaryocytes. RESULTS: A marked 2- to 3-fold increase in trabecular bone volume and bone formation indices were observed in these mice. A 20- to 150-fold increase in trabecular bone volume was measured for the entire femoral medullary canal. The increased bone mass phenotype in these animals was not caused by osteoclast defects, because osteoclast number and function were not compromised in vitro or in vivo. In contrast, in vivo osteoblast number and bone formation parameters were significantly elevated. When wildtype or mutant osteoblasts were cultured with megakaryocytes from GATA-1- or NF-E2-deficient mice, osteoblast proliferation increased over 3- to 6-fold by a mechanism that required cell-to-cell contact. CONCLUSIONS: These observations show an interaction between megakaryocytes and osteoblasts, which results in osteoblast proliferation and increased bone mass, and may represent heretofore unrecognized anabolic pathways in bone.

Alkaline Phosphatase↗